rear main leak

[bob keenan]

we have a scat crankshaft and one piece seal from snyders installed after the block was line bored and all clearances checked.an oil leak the size of a quarter developed from the rear main area . are there any more fixes or do we live with it? engine is still on the motor stand.

[Bob Bidonde]

Try running the engine with a shortened rear main oil tube. Shorten the tube so its exit is above the crankcase oil level. My theory is that the oil cannot drain fast enough because the exit of the tube is submerged, so the oil backs-up and overflows out of the rear main bearing.

[old31]

Is there any reason the tube must be below the oil?

[Benson]

Actually as Bob Keenan's question in post #1 is worded, does his modified engine use the dip tube?

Does THIS modified seal modification remove the tube since the slinger is no longer involved?

[Benson]

Originally Posted by Bob Bidonde

Try running the engine with a shortened rear main oil tube. Shorten the tube so its exit is above the crankcase oil level. My theory is that the oil cannot drain fast enough because the exit of the tube is submerged, so the oil backs-up and overflows out of the rear main bearing.

On a stock engine: The tube MUST be below the oil level to prevent the crankcase pressure from forcing the oil out the rear main.


That is the whole purpose of the tube ...

Lets see what the engine rebuilders say ....

[rotorwrench]

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Does this block still have babbitt or has it been converted to inserts?.

I've have not used one of these seals since I prefer slingers where they were the original seal system but I have read the process of installing these seals and it doesn't cut you much slack. The main bearing clearances have to be at minimum clearance according to instructions and that can be difficult to do. The slinger machining has to be as large as it can be made within the range that they have in the instructions. I assume that this crank was already machined by Scat. If it was, what was the seal surface diameter? if too small, it allows for more movement of the seal in service. They have to be bonded well to the retainers too. If it spins in the retainers, it will leak.

Other considerstions are flywheel/clutch balance, modifications to clutch & flywheel, and engine to transmission alignment. I would assume it is being run with at least the clutch & flywheel mounted.

Some engines use a two piece seal but most of them are modified a good bit. You might just run it under load in the car for a while and see what happens. The leak might go away after the seal wears in a bit.

Old Fords have a tendency to mark there spot no matter how hard we try to keep them from it.

[Bob Bidonde]

I have been running a rear main bearing drain tube out of the oil and it is not effected by the crankcase environment. Another myth is that the oil pump creates a suction on the submerged tube.

[johnneilson]

Rear main seal leaks can come from many places.
If mains are babbit and shimmed, is there sealant to prevent seepage between cap and block? Inserted motors can leak here if pressure is high and not vented properly. (main bolts are another place to look)
If pressurized, I have seen cam leakage mistaken for main.
If cap is drilled for alignment pins and split pin or roll pin used will leak.


The SCAT cranks are available with and without rear seals, those with are 2 pc chevy seal. Typically, those do not leak, unless installed incorrectly. I have seen pictures on the web showing the incorrect installation. Those seals have a very wide margin of error for concentricity and diameter.


One last caution, if a "B" motor and high oil pressure, have seen side cover weeping and oil runs along the pan rail to rear of motor.


Merry Christmas, J

[bob keenan]

thanks,I will try that

[bob keenan]

tube is still there

[bob keenan]

crank is machined,flywheel and front pulley are balanced.rear seal was installed with a small amount of right stuff rtv

[bob keenan]

thank you

[Kohnke Rebabbitting]

Originally Posted by Benson

On a stock engine: The tube MUST be below the oil level to prevent the crankcase pressure from forcing the oil out the rear main.


That is the whole purpose of the tube ...

Lets see what the engine rebuilders say ....

" AGREE "

With the turbulence of the oil pump, and oil moving past the end of the pipe, it keeps the oil going down the tube.

How much end play do you have?

How much oil clearance do you have ?

What year is the motor ?

Herm.

[Dave in MN]

I have assembled and bench run many engines and my experience with oil leaks: If it leaks while on the test stand with no substantial load, it will leak worse once loaded. My testing and breaking in of engines with a dynometer has lead me to this conclusion. I think you will experience the same leak or worse once you install your engine and start driving the car.

At this point, it is pretty easy to drain the oil, remove it from the stand, mount it to an engine stand and rotate it pan side up. Remove the flywheel and check the path of the oil on the cap, the surfaces of the flywheel housing and carefully look at the rear of the pan where it meets the pan rail. Any traces of oil on these surfaces should be noted. Remove the pan and look for traces of oil getting past the pan gaskets. (including the cork gasket at the rear cap)
Added: Download the one piece seal installation instructions from the Snyder's website and verify the seal is installed correctly. Pressure test the seal. If the seal is the cause, it should show...

If the seal is not leaking, look for traces of oil at all exposed areas of the rear main bolts. Remove the main bolts and again check for oil on their surfaces. Try to remove the rear cap without rocking it..lift it straight up and look for any paths of oil across or around the shims or mating surfaces at the block and cap. If you discover any oil paths you have likely located the source of the leak.

I agree with Herm regarding the rear main oil drain tube. Leave it stock length.
Good Day!

www.durableperformance.net

[Terry Burtz, Calif]

After you remove the oil pan, don't do anything until you pressurize the rear main drain tube with oil and look for leaks.

This is the last step in the instructions before the oil pan is installed.

[Benson]

Originally Posted by Terry Burtz, Calif

After you remove the oil pan, don't do anything until you pressurize the rear main drain tube with oil and look for leaks.

This is the last step in the instructions before the oil pan is installed.

Is 10 lbs air pressure enough or too much?

I do not have instruction sheet...

Thanks...

I wish that I had found this seal in 1976 when we were building the B block with pressure mains and rods ... !

[Terry Burtz, Calif]

Benson,

It's better to use pressurized oil instead of air because oil is very visible.

You can go up to 50 psi if using a one-piece seal with the insert from Dan Price (dan4banger.com). The seal design is a radial lip and seals tighter with increased pressure. Try to rig up something like a hydraulic brake bleeder. If using the 2 piece design, I would not use more than 10 psi.

I also make Model A seals that are a similar design. They are one-piece only. Some years ago, one of these seals would leak after being driven fast on the freeway, but wouldn't leak if driven at normal speeds. When the pan was removed and the drain tube pressurized with oil to 50 psi to find the leak, there was no leak.

The engine used a Burlington crankshaft had been machined to provide the seal rubbing surface. The seal rubbing surface was verified to be concentric with the rear main bearing. Next, the crankshaft was drilled to get oil pressure from the mains to the connecting rods, and the engine was assembled and the rear main drain tube was pressure checked and verified that there were no leaks.

When the engine was completely taken apart, the seal rubbing surface was found to have .011 inch runout (tir). The seal instructions specify .001 inch tir.

When the crankshaft was drilled, stresses were relieved and the crankshaft was no longer straight. The crankshaft was straightened and the engine ran good with no leaks until the crankshaft broke at connecting rod journal 4.

[Terry Burtz, Calif]

Benson,

I just re-read your post, and see that you don't have the instructions. They are copied below without the figure.


1) Two seals are supplied. The larger seal fits into the groove of the rear main cap (B-6327), and the smaller seal fits into the groove of the block insert (B-6335). The smaller seal will not fit properly in a poorly made reproduction block insert.
2) If desired, a replacement block insert with a groove identical to rear main cap groove can be made or purchased. In this case, discard the smaller seal and upon assembly, lubricate and carefully slip the seal over the flywheel mounting flange. A plastic sandwich bag placed over the flange will protect the seal from damage due to small burrs.
3) Thoroughly clean the grooves in the rear main bearing cap (B-6327) and block insert (B-6335) to remove all traces of dirt and oil, which may interfere with proper seal installation and sealant adhesion. Also, make sure rear main cap drain pipe is clear
4) Seat each seal with lip pointing towards front of engine (see figure) into its respective groove, and trim the ends slightly long to provide “crush” at the mating surface. A single edge razor blade and stationary disk sander work well for trimming and squaring the ends. Cut the pieces to be used long, and experiment with trimming and squaring operations on the cut off pieces.
5) Without the crankshaft in place, assemble the seal with its lip facing towards front of engine, shims, block insert, and rear main cap to the engine. Check to be sure the seal fits properly in its grooves, and is not distorted or offset relative to the rear main bearing.
6) Machine the rear slinger area of crankshaft as shown in the figure. Finished diameter shall be between 2.330 in. and 2.370 in., and concentric with the rear main journal within .001 in. to prevent whipping of the seal lip outward. Machine crankshaft to largest diameter between limits consistent with cleanup. Polish seal contact area of crankshaft to a bright smooth finish. Main bearing clearance must be between .0010 in. and .0015 in. to keep the crankshaft from whipping the seal lip outward. On final assembly, apply either an RTV silicone adhesive or Permatex #2 sparingly to both grooves and all mating surfaces where shims, rear main cap, block insert, and block meet. Avoid getting adhesive on seal lip. Also apply sealant to rear main bolts.
7) Before installing oil pan, and after adhesive has cured, test seal and rear main cap area for leakage by pressurizing the rear main cap drain pipe with motor oil to 10 psi and check for leaks.
8) If a Model B engine that has been modified to provide pressure to the connecting rods (drilled crankshaft) is using this seal, an additional oil pressure check should be done by pressurizing the rear main bearing groove that supplies connecting rod #4 to the anticipated pressure (40 psi?). If a leak occurs, it will usually be between the groove in the rear main bearing feeding rod #4 and either thru the shims or up or down the rear main bolts.

[Benson]

Thanks to all that responded.

Good info I will have to digest all of the info...

Thanks for all of the work answering questions.

On the 1976 engine we tried:

The first thing we did was to reduce COLD engine oil pressure from 100 lbs. to about 25 lbs with a bypass on oil pump.

The following seals:

1. cork

2. rope

3. Silicone rubber

4. another rubber type that I do not remember anymore.

This engine had several cracks that were stitched.

Finally when the bill reached three times the rebuild cost of a stock Model B engine I abandoned the project.

More problems surfaced to prompt the abandoning of project.

We built a stock B block.